Research Horizons

Swimming Through Sand

Shovel nosed snake photo: Jason Maderer

For swimming through sand, a slick and slender snake can perform better than a short and stubby lizard.

That’s one conclusion from a study of movement patterns in the shovel- nosed snake, a native of the Mojave Desert of the southwest United States. The research shows how the snake uses its slender shape to move smoothly through the sand, and how its slippery skin reduces friction. Both factors provide locomotive advantages over another sand-swimmer: the sandfish lizard native to the Sahara Desert of northern Africa.

The study provides information that could help explain how evolutionary pressures have affected body shape among sand-dwelling animals. And the work could also be useful in designing search-and-rescue robots able to move through sand and other granular materials with a minimal expenditure of energy.

Using X-ray technology to watch each creature as it moved through a bed of sand, researchers studied the waves propagating down the bodies of both the snakes and sandfish lizards. Granular resistive force theory, which considers the thrust provided by the body waves and the drag on the animals’ bodies, helped model the locomotion and compare the energy effciency of the limbless snake against that of the four-legged lizard, which doesn’t use its legs to swim through the sand.

“We were curious about how this snake moved, and once we observed its movement, how it moved so well in the sand,” said Dan Goldman, an associate professor in the Georgia Tech School of Physics. “Our model reveals how both the snake and the sandfish move as fast as their body shapes permit while using the least amount of energy.”

Supported by the National Science Foundation and the Army Research Office, the research was reported in the Journal of Experimental Biology.—JOHN TOON

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